Transforming growth factor-B1 (TGF-Bl) appears to play a major role in the development of atherosclerosis. TGF-Bl is expressed in atherosclerotic human arteries and has potent effects on vascular cells. However, it remains controversial whether TGF-B1 causes or protects against atherosclerosis. This application includes a series of investigations, performed in mice, that will elucidate whether TGF-B1 is pro- or anti-atherogenic. The investigations will also identify mechanisms by which TGF-B1 expression is regulated. Three specific aims are proposed: (1) To determine the mechanisms through which TGF-B1 promotes neointimal growth in uninjured mouse arteries and to identify mechanisms by which TGF-B1 expression is regulated. (2) To determine whether elevations in systemic or arterial wall TGF-Bl accelerate atherogenesis, and to test whether increased TGF-B1 expression alters extracellular matrix and lipid accumulation, vascular cell proliferation, and PAI-1 expression. (3) To test the hypothesis that loss of the type II TGF-B receptor (tgfbr2) in smooth muscle cells, with concomitant loss of TGF-B1 signaling, retards the development of atherosclerosis. The specific aims will be accomplished using the complementary strategies of in viva gene transfer to the artery wall and germ line manipulations. In aim 1, increasing TGF-B1 expression in the mouse carotid artery by gene transfer is expected to promote intimal growth. Specific assays will identify the mechanisms by which this growth occurs. Aims 2 and 3 take complementary approaches of overexpression and loss of function, achieved by germ line manipulation of the TGF-B1 and its specific receptor, tgfbr2. In aim 2 TGF-B1 expression will be increased either systemically (in plasma) or locally (in the artery wall). In aim 3, the effects of TGF-B1 on the artery wall will be blocked by disrupting TGF-B1 signaling in smooth muscle cells. In both aims 2 and 3, the effect of the manipulations on the development of atherosclerosis will be measured. The proposed experiments will define the effects of TGF-B1 on the phenotype of normal and atherosclerotic arteries, elucidate the molecular and cellular mechanisms by which these effects are produced, and clarify the mechanisms through which TGF-B1 expression in the artery wall is regulated. The results of these investigations will reveal whether strategies aimed at blocking the actions of TGF-B1 on the artery wall represent promising approaches to the prevention and treatment of atherosclerosis.